Field of the Invention
The present invention relates to a method and apparatus for controlling synchronization of camera shutters in an in-vehicle Ethernet communication network and, more particularly, to a method and apparatus for controlling synchronization of camera shutters in an in-vehicle Ethernet network to operate shutters of all cameras inside a vehicle in synchronization based on IEEE 802.1AS.
Discussion of the Related Art
Vehicles on the market today have a variety of electronic controllers (ECUs) for improving convenience and safety of drivers, and are basically configured with an in-vehicle network for communication among these ECUs.
Particularly, as in-vehicle ECUs are gradually increased in number and are capable of interacting with various external devices, overload of an existing vehicle network and increase in costs related to wiring harnesses are caused.
In addition, as customer demands for high-quality audio/video (AV) data and applications using AV data are increased, the need for bandwidth extension is getting more serious.
As such, a large number of vehicle manufacturers consider Ethernet for in-vehicle networking, and some vehicle manufacturers have recently produced Ethernet-based around view monitor (AVM) systems.
An Ethernet network generally includes a plurality of local area networks (LANs) and a plurality of bridges for connection among the LANs.
Ethernet is characterized in that multiple nodes competitively attempt to access a common medium using a Carrier Sense Multiple Access/Collision Detection (CSMA/CD) protocol. However, the CSMA/CD scheme provides the same priority to all traffic, thus making a plurality of nodes transmit traffic thereof through competition, and thus is not appropriate for transmission of multimedia data which is sensitive to propagation time delay, e.g., AV data.
Accordingly, Ethernet uses a technology of synchronizing timings of all network nodes to transmit the multimedia data.
Currently, a standard for audio/video bridging (AVB) is being developed as a transport protocol layer standard such as IEEE 1722 to transmit an AV signal which is sensitive to streaming time. Specifically, the goal of the AVB standard is a quality-guaranteed transmission technology for appropriate transmission of a multimedia stream, e.g., an AV stream, over Ethernet.
As described above, a conventional LAN and, more particularly, a representative technology thereof, Ethernet, have basically used a frame-based packet switching technology and thus could not easily provide an efficient and quality-guaranteed transmission technology. To solve this problem, AVB has been initially developed by IEEE 802.2 under the name of synchronous Ethernet, residential Ethernet, or the like. Currently, IEEE 802.1 is conducting research on a method for implementing a similar technology on a bridge without significantly undermining the paradigm of conventional non-synchronous packet switching.
Basically, AVB of IEEE 802.1 is a technology for enabling synchronous traffic transmission using conventional Ethernet bridges performing packet switching, and a core thereof is to synchronize clocks of bridges within a certain geographic range. If the clocks of the bridges are synchronized, a certain-sized Ethernet frame can be transmitted among the bridges with a certain time interval exactly at a desired time. This basic concept can be expanded to a bridge mesh which can be used as infrastructure for stably delivering synchronous traffic.
For example, IEEE 1588 precision time protocol (PTP) is a time synchronization standard operable over open systems interconnection (OSI) layers, and IEEE 802.1AS is a time synchronization standard supporting only the profile of OSI layer 2, i.e., a data link layer, based on IEEE 1588. If IEEE 802.1AS is applied to a layer 2 device such as a bridge or a switch, an OSI layer 2 time synchronization network may be configured.
A time synchronization method among devices according to IEEE 802.1AS is a method for synchronizing a transmitter and a receiver using a time stamp including time synchronization information. In this method, a grandmaster (GM) for providing a reference time for time synchronization is selected among devices in a network, a local time of the selected grandmaster is transmitted to other devices using an announce message, and thus the other devices use the local time of the grandmaster as a reference time. At this time, the grandmaster transmits the announce message to all other devices to signal information indicating the presence of the grandmaster and a comparative value indicating the suitability as a reference time providing device.
That is, the grandmaster is a top node of the IEEE 802.1AS timing tree and periodically transmits current time information to sub nodes.
IEEE 802.1AS defines a procedure for determining a grandmaster and acquiring time synchronization, a procedure for discovering all devices on a network and controlling access to links using a plurality of control messages, and a procedure for persistently checking link states using an announce message.
However, conventional in-vehicle Ethernet cameras attempt to capture images at the same time based on time synchronization of IEEE 802.1AS, but cannot easily acquire exactly equal-time images due to shutter asynchrony.